Two estrogen receptors have been described in reproductive tissue of chicks and humans which have equilibrium dissociation constants for estradiol of 0.1nM and 4nM and are present in relative concentrations of 1:4 respectively. These differ from the Type I and Type II estrogen binding proteins described in the rat (Clark, et al., 1978) since both are translocated to the nucleus on administration of estrogen. Furthermore, both receptors in the chick appear to be involved in ovalbumin mRNA synthesis. The high affinity receptor has been purified to homogeneity and appears to increase RNA polymerase II activity in chick oviduct nuclei. It is the purpose of this proposal to purify the lower affinity receptor and to investigate the effects of both receptors individually and in concert, on ovalbumin mRNA synthesis in vitro. By using specific probes for transcription of the 3' end of the gene, the possible effect of the receptor on initiation and/or elongation of ovalbumin mRNA will be assessed.